I thought Dictionary.com wasn't availabe as a search engine plug-in in the Firefox browser search toolbar so I kept on using the Answers.com and/or the Webster search engines, but today, I finally looked, and there it was, Dictionary.com, Thesaurus.com, and Reference.com (the encyclopedia) ready to be installed with a click. Lesson? Just look for it immediately!

You may also find other Firefox search engine plug-ins here and here.